1. Field of the Invention
This invention relates in general to a registration control system for a printed label cutoff apparatus and in particular to a registration control system capable of making both phase and base speed adjustments to the cutoff apparatus.
2. Description of the Prior Art
A printed label cutoff machine typically includes a pair of feed rolls for moving a sheet of printed labels continuously between a pair of cutting wheels. The cutting wheels generally include at least one cutting blade which makes a single transverse cut along the sheet during each revolution thereof. The particular point at which the labels are to be severed is defined by a registration mark or an eyemark printed on the sheet along with the printed portion of the labels. Most prior art registration control systems utilize an optical scanner positioned adjacent the printed sheet which produces a pulse whenever a registration mark passes the scanner. Generally, the location of the cut is controlled by controlling the speed at which the labels are fed through the cutting rolls. Alternatively, the cut location can also be controlled by controlling the speed of rotation of the cutting rolls.
An example of a prior art registration control system is disclosed in U.S. Pat. No. 3,774,016 to Sterns et al. The control system includes an optical scanner for detecting a registration mark, and a knife cut detector for producing a knife pulse whenever the cutting wheels produce a knife cut. In addition, the system includes a measuring wheel which rides on the web to produce a series of pulses as the web moves along so that each pulse corresponds to a given distance of web movement. A number proportional to the distance between the scanner and the location where a registration mark should be when a proper knife cut is to be made is preset manually into a counter. The number loaded into the counter represents the number of measuring wheel pulses which should occur between the detection of a registration mark and the occurrence of a knife pulse.
Each time a scanner pulse is generated, the control opens a gate which allows the measuring wheel pulses to be applied to a count down terminal of the counter. The occurrence of the knife pulse freezes the count. If the knife pulse occurs before the counter has counted down fully, the remaining count in the counter represents the deviation or distance the cut was short. On the other hand, if the knife pulse occurs after the counter counts down to zero, the counter is switched to the up counting mode until the knife pulse occurs. In this case, the count in the counter represents the deviation or distance the cut was long. The control system utilizes the measured deviation of the cut location to generate an individual deviation correction signal to adjust the speed of the cutting wheels through a differential mechanism for the next cut. The control also processes the measured deviation with previously obtained deviation measurements to generate an average deviation correction signal to further adjust the speed of the cutting wheels for the next cut.
Another prior art registration control system is manufactured by Econ Corporation as Model No. 820. The Econ system can control a label cutoff machine which includes means for adjusting both the length of the individual labels, and the location of the cut. These two adjustments are typically referred to as a base speed adjustment and a phase adjustment respectively.
The Econ system utilizes a special encoder coupled to the cutting wheels which produces a predetermined number of pulses and a single reference pulse per revolution of the cutting wheels. The encoder includes means for adjusting the point of revolution at which the reference pulse is generated. The duration of the reference pulse defines a window area in which the scanner is expected to see an eyemark. The difference between the occurrence of a reference mark and the occurrence of a scanner pulse is measured in terms of encoder pulses. This difference represents the phase error and is used to produce a phase correction signal for making a phase adjustment. In the Econ system, if the eyemark is detected outside the designated window area, the control is lost and cannot automatically bring the machine into registration. The operator must then use manual controls to bring the machine into registration.
The Econ control monitors the individual phase errors to determine whether a base speed adjustment should be made. If the phase error exceeds an operator selected threshold for an operator selected number of consecutive labels, the control will adjust the base speed by a preset amount, without reference to the actual amount of phase error. Thus, if the phase errors for the required number of labels have each exceeded the threshold by a relatively large amount, the same base speed adjustment is made as if the phase errors have each just exceeded the threshold by a relatively small amount.